It is known to use a burner assembly to heat and dry aggregate materials used in connection with the production of hot mix asphalt. See, e.g., U.S. Pat. No. 5,700,143, No. 5,511,970, No. 4,559,009 and No. 4,298,337. However, conventional burner assemblies suffer from several disadvantages. For example, conventional burner assemblies are incapable of producing a flame configuration satisfactory for asphalt production in a variety of different-sized combustion chambers. As a result, conventional burner assemblies typically include adjustable spin vanes or spin racks to accommodate different-sized combustion chambers. For example, U.S. Pat. No. 6,488,496 of Feese et al. describes a compact combination burner with an adjustable spin rack. Adjustable spin vanes, however, increase the cost of manufacture and maintenance and the amount of labor required to operate the burner. In addition, conventional burner assemblies do not adequately mix combustion air with fuel such as natural gas and/or vaporized liquid propane. As a result, conventional burner assemblies produce unwanted levels of harmful CO, NOx, CO2 and VOC emissions.
It would be desirable, therefore, if an apparatus could be provided that would selectively fire on gaseous fuel, liquid fuel, or both gaseous and liquid fuel. It would also be desirable if such an apparatus could be provided that would fire on gaseous and/or liquid fuels without physically altering the components of the apparatus, changing the firing rate of the apparatus, or shutting down the apparatus. It would be further desirable if such an apparatus could be provided that would fire on oil or liquid propane without changing the atomizing nozzle. It would be still further desirable if such an apparatus could be provided that would supply natural gas or propane around the atomizing nozzle for use as pilot fuel. In addition, it would be desirable if such an apparatus could be provided that would produce a stable flame configuration having a short flame length and a narrow flame diameter adapted for use on a wide variety of different-sized combustion chambers. It would also be desirable if such an apparatus could be provided that would more completely and uniformly mix fuel and air in order to obtain more rapid combustion and improve combustion intensity, thereby reducing the combustion space required in the asphalt drum. It would be further desirable if such an apparatus could be provided that would more adequately mix combustion air with fuel such as natural gas and/or vaporized liquid propane such that levels of harmful CO, NOx, CO2 and VOC emissions are minimized. In addition, it would be desirable if such an apparatus could be provided that would be capable of firing on low excess air pre-mix gas. It would also be desirable if such an apparatus could be provided that would produce a stabilizing gas base flame. It would be further desirable if such an apparatus could be provided that would reduce the temperature of the dryer drum breech plate where the burner is mounted. It would be still further desirable if such an apparatus could be provided that would eliminate the need to adjust spin vanes to achieve a desired flame configuration. It would also be desirable if such an apparatus could be provided that would be less complicated and expensive to manufacture, operate and maintain than conventional burners.